The present invention pertains to a coated cemented carbide milling insert, particularly useful for either wet or dry machining of cast iron, such as nodular cast iron (NCI), grey cast iron (GCI), austempered ductile iron (ADI) and compacted graphite iron (CGI), where a high wear resistance and an excellent resistance against thermo cracks are required.
Cast irons have a machinability that can vary considerably between the various groups but also within a certain group. The tool life may be influenced significantly by a small variation in the chemical composition and/or the microstructure within the material. These variations may be related to the casting technique used, such as the cooling conditions. Cast irons are frequently machined with coated cemented carbide inserts using some kind of coolant, and the associated thermal cycling when the insert enters and exits the work piece, normally generates thermally induced cracks in the cutting edge perpendicular to the edge line, so called comb cracks. These comb cracks grows into the substrate and eventually cause chipping and deterioration of the cutting edge.
Cast irons are also very demanding when it comes to wear resistance due to non-metallic inclusions and/or cast skin, and therefore CVD-coated inserts have been commonly used, e.g. according to U.S. Pat. Nos. 5,912,051, 5,942,318, 6,767,583.
WO 2006/043421 discloses cemented carbides which include WC having an average particle diameter of 0.3 μm or less as a hard phase and 5.5 to 15 wt-% of at least one iron group metal element as a binder phase, and comprise, in addition to the above hard phase and binding phase, 0.005 to 0.06 wt-% of Ti, Cr in a weight ratio relative to the binder phase of 0.04 to 0.2, and the balanced amount of inevitable impurities. Especially, the cemented carbides contain no Ta.
U.S. Pat. No. 5,912,051 discloses a coated cutting insert particularly useful for dry milling of grey cast iron.
In U.S. Pat. No. 6,062,776 is disclosed a coated cemented carbide cutting tool particularly designed for the wet and dry milling of workpieces of low and medium alloyed steels or stainless steels, with or without abrasive surface zones, in machining operations requiring a high degree of toughness of the carbide cutting edge. The external cutting conditions are characterized by complex shapes of the workpiece, vibrations, chip hammering, recutting of the chips etc.
In U.S. Pat. No. 6,177,178 is disclosed a coated cemented carbide cutting tool particularly designed for the wet and dry milling of low and medium alloyed steels.
WO 01/16388 discloses a coated insert particularly useful for milling in low and medium alloyed steels with or without abrasive surface zones during dry or wet conditions at high cutting speed, and milling hardened steels at high cutting speed.
U.S. Pat. No. 6,638,609 discloses coated milling inserts particularly useful for milling of grey cast iron with or without cast skin under wet conditions at low and moderate cutting speeds and milling of nodular cast iron and compacted graphite iron with or without cast skin under wet conditions at moderate cutting speeds.
US Patent Application 2006/0115683 discloses coated milling inserts particularly useful for milling of grey cast iron with or without cast skin under dry conditions at preferably rather high cutting speeds and milling of nodular cast iron and compacted graphite iron with or without cast skin under dry conditions at rather high cutting speeds. The inserts are characterised by a WC—Co cemented carbide with a low content of cubic carbides and a highly W-alloyed binder phase and a coating including an inner layer of TiCXNy with columnar grains followed by a wet blasted layer of α-Al2O3.